The present invention relates to methods and apparatuses for assisting vehicle operator braking action of a vehicle.
To enhance safety of a car and passengers in present-day road traffics, efforts are being made to support the operator in routine driving operations.
In this direction, antilock braking systems (ABS) have been proposed and adopted to enhance longitudinal vehicle stability in dynamically critical conditions in braking process.
xe2x80x9cAutomatic distance regulationxe2x80x9d (ADR) systems have been proposed that are intended to detect and carry out a controlled braking action to control the distance of a vehicle from other vehicles and/or stationary objects in the direction of vehicle motion. JP-A 7-144588 discloses a system whereby traveling speed and deceleration of a vehicle in front are determined using a Doppler sensor and a vehicle speed sensor, which are on a vehicle to be controlled, and a safe distance from the vehicle in front is determined in response comparison of the traveling speed of the vehicle in front with a predetermined value of 15 km/h. In this system, a driver is warned and an automatic braking action is initiated if the distance from the vehicle in front becomes less than the safe distance.
Other systems have been proposed that are intended to initiate braking action before the operator of a vehicle initiates braking action. JP-A 6-24302 discloses a system whereby, when a foot of the operator leaves an accelerator pedal, two micro switches are both closed to energize a solenoid for activating a brake pedal. Energizing the solenoid pulls the brake pedal to partially activate a braking system before the foot of the operator is stepped on the brake pedal.
A disadvantage of such systems as disclosed in JP-A 7-144588 and JP-A 6-24302 is that the correction of the motion of a vehicle takes place consistently and with no opportunity for the operator to exercise control. Because of the requirements of the regulating algorithm, a controlling action by such systems will take place quite early so that the braking action need not be executed too abruptly. Hence, the systems will respond even in situations that a practiced operator would have negotiated himself with no problems. As a result, the operator will experience a repeated automatic intervention in the control of the vehicle, which is actually necessary in only a few cases from his or her point of view, and will consider such intervention as unwarranted interference so that such systems are unlikely to meet with much acceptance.
Accordingly, it is an object of the present invention to provide a vehicle operator braking action assisting method and apparatus, which overcome the disadvantage of the prior art.
Another object of the present invention is to provide a method and apparatus of this kind that will prevent a vehicle operator from considering a repeated automatic intervention in the control of the vehicle as unwarranted interference without sacrificing the advantages of a vehicle operator braking action assisting system.
For this purpose, in a method or an apparatus according to the present invention, a detection system on a vehicle to be controlled detects obstacles, which are in or near the direction of motion of the vehicle, and provides corresponding data to a control unit. In addition, the vehicle has, or certain of its components are provided with, vehicle condition sensors for detecting characteristic parameters of the condition or state of motion of the vehicle and transmitting data regarding these parameters to the control unit, and vehicle operator demand sensors for detecting characteristic parameters of the power or brake demand of the operator and transmitting data regarding these parameters to the control unit. From the data reported concerning the obstacles, the vehicle condition parameters and the operator demand parameters, the control unit ascertains a whether a braking action by the vehicle operator is needed. The control unit determines a target stand-by brake pressure and generates a command for adjustment of brake pressure to the target stand-by pressure. The apparatus includes a braking system operable by the vehicle operator. The braking system has a temporary stand-by state in which brake pressure is adjusted toward the target brake pressure. The braking system is operable to make a shift to the stand-by state only after the control unit has determined that braking action by the vehicle operator is needed. In the stand-by state, the brake pressure as high as the target stand-by brake pressure actuates the brake, producing minimum possible vehicle deceleration. Since the brake pressure will drop to zero or disappear upon termination of the stand-by state and the vehicle deceleration produced in the stand-by state is at required minimum level unnoticeable by the vehicle operator, the vehicle operator is prevented from considering such an automatic intervention in the control of the vehicle as unwarranted interference without sacrificing the advantages of a vehicle operator braking action assisting system.
It is especially advantageous if the apparatus includes an antilock braking system and/or an electronic dynamic regulating system, since in that case the motion of the vehicle will be more controllable even during braking and under critical road conditions. Since such systems are now standard equipment in many vehicles, the apparatus for assisting vehicle operator braking action may advantageously be combined with or integrated into such conventional systems.
The arrangement for detecting the condition of the vehicle includes sensors for detecting traveling speed of the vehicle (or vehicle speed) and weight of the vehicle.
The arrangement may include sensors and a control unit to determine the coefficient of force transmission, i.e., the traction, between the vehicle tires and the roadway, so that the prevailing road conditions can be detected. In this way, readings for maximum possible target stand-by brake pressure can be so derived, which may be subject to variations even during the temporary stand-by state, for example if the roadway is wet or slippery.
As sensors for detection of power or brake demand of the vehicle operator, conventional sensors for detecting whether a brake pedal of the braking system is depressed or released and for detecting stroke of an accelerator pedal are used.
As sensors for detection of the obstacles located in or near the direction of motion of the vehicle, conventional radar sensors employing laser, whose application is familiar to those skilled in the art, are used, However, any other types of sensors that permit an adequate preview of the range of motion of the vehicle and which are suitable for service under rough vehicle condition may be used.
In one embodiment, the control unit continuously detects a traveling speed of a vehicle to be controlled and continuously calculates a distance from a vehicle in front, relative speed, and a criterion distance based on the traveling speed, the distance and the relative speed. If the criterion is transgressed, i.e., the distance becomes equal to or less than the criterion distance, the control unit determines that braking action by the vehicle operator is needed and triggers stand-by brake pressure regulation in the temporary stand-by state. The stand-by state is terminated when the control unit subsequently determines depression of the brake pedal or when the control unit subsequently determines that the distance from the vehicle in front becomes greater than the criterion distance. In the stand-by state, the control unit continuously determines the target stand-by pressure as a function of the traveling speed and weight of the vehicle, and the brake pressure as high as the target stand-by pressure is applied to the brake. According to this function, the target stand-by pressure is relatively high at higher speeds, while it is relatively low at low speeds, and at intermediate speeds, with the same speed, the target stand-by pressure becomes higher as weight of the vehicle becomes heavier. The target stand-by pressure so derived provides vehicle deceleration, which is less noticeable to the vehicle operator in the stand-by state.
In a further embodiment, after determining that braking action by the vehicle operator is needed, the control unit determines the state of emergency of imminent braking action based on release speed of accelerator pedal in its stroke toward its release position. If the accelerator pedal is released after the control unit has determined that braking action by the vehicle operator is needed, in the stand-by state, the control unit continuously determines the instantaneous release speed of the accelerator pedal in its stroke toward its released position to find out the maximum release speed of the accelerator pedal and determines target stand-by pressure as a function of the maximum release speed of accelerator pedal and weight of the vehicle, and the brake pressure as high as the target stand-by pressure is applied to the brake. According to this function, the target stand-by pressure is relatively high at relatively high emergency, while it is relatively low at low emergency, and at intermediate emergency, with the same degree of emergency, the target stand-by pressure becomes higher as weight of the vehicle becomes heavier. The target stand-by pressure so derived provides vehicle deceleration of satisfactorily high level immediately after depression of the brake pedal.
In a still further embodiment, a control unit continuously detects a traveling speed of a vehicle to be controlled and continuously calculates a distance from a vehicle in front, relative speed, and a target deceleration based on the traveling speed, the distance and the relative speed. The target deceleration is deceleration at which the vehicle is to be decelerated to maintain a minimum spacing with the vehicle in front. If the target deceleration becomes greater, in magnitude, than a preset criterion deceleration (0.6G in this example), the control unit determines that braking action by the vehicle operator is needed. Then, control unit determines whether or not the accelerator pedal is depressed. If the accelerator pedal is not depressed upon or immediately after determination that the target deceleration is greater than the criterion deceleration, the control unit initiates temporary stand-by state. The stand-by state is terminated when the control unit subsequently determines depression of the brake pedal or when the control unit subsequently determines depression of the accelerator pedal. In the stand-by state, the control unit determines once a reading of the traveling speed upon determining that the accelerator pedal is not depressed after determining that braking action by the vehicle operator is needed, The control unit determines the target stand-by pressure as a function of the reading of the traveling speed of the vehicle and the vehicle weight, and the brake pressure as high as the target stand-by pressure is applied to the brake. If, subsequently, the brake and accelerator pedal are left at their released positions, respectively, the target stand-by pressure so derived is unaltered for a preset period of time (1 second in this example) and then drops toward zero level at a gradual rate or immediately.
In a still another embodiment, the control unit incorporates, in calculation of the target stand-by brake pressure, currently determined coefficient of force transmission, i.e., the traction, between the vehicle tires and the roadway so that the target stand-by brake pressure becomes low as the coefficient becomes small
In a still further embodiment, the control unit incorporates, in calculation of the target stand-by brake pressure, currently determined speed ratio in the transmission so that the target stand-by brake pressure becomes high as the speed ratio decreases. In this case, the target stand-by pressure is at the maximum level at the first speed ratio. As the speed ratio increases toward the direct drive, the target stand-by brake pressure becomes low. Altering the target stand-by pressure in this manner has the advantage that deceleration due to the target stand-by pressure is less perceived by the vehicle operator in the circumstance of deceleration due to engine braking process.
It is of advantage if the environmental data from the obstacle detection system and/or the signals from vehicle condition sensors and operator demand sensors are stored in a memory. This has the advantage that the parameters leading to initiating stand-by state for braking function are available for subsequent analysis and especially desirable to the manufacture of the motor vehicles for reasons of product liability analysis.
It is of advantage if a camera, which is preferably mounted in the region of the inside rear view mirror of the vehicle, is provided so that an accident event can be observed visually and the video signal generated by the camera can be stored in the memory. Providing such a camera has the advantage that an accident event can be analyzed from the point of view of the driver and subsequently evaluated.